The only fact the Guardian can report is that the case involves the London solicitors Carter-Ruck. Photograph: John D McHugh/AFP

The Guardian has been prevented from reporting parliamentary proceedings on legal grounds which appear to call into question privileges guaranteeing free speech established under the 1688 Bill of Rights.

Today's published Commons order papers contain a question to be answered by a minister later this week. The Guardian is prevented from identifying the MP who has asked the question, what the question is, which minister might answer it, or where the question is to be found.

The Guardian is also forbidden from telling its readers why the paper is prevented – for the first time in memory – from reporting parliament. Legal obstacles, which cannot be identified, involve proceedings, which cannot be mentioned, on behalf of a client who must remain secret.

The only fact the Guardian can report is that the case involves the London solicitors Carter-Ruck, who specialise in suing the media for clients, who include individuals or global corporations.

The Guardian has vowed urgently to go to court to overturn the gag on its reporting. The editor, Alan Rusbridger, said: "The media laws in this country increasingly place newspapers in a Kafkaesque world in which we cannot tell the public anything about information which is being suppressed, nor the proceedings which suppress it. It is doubly menacing when those restraints include the reporting of parliament itself."

The media lawyer Geoffrey Robertson QC said Lord Denning ruled in the 1970s that "whatever comments are made in parliament" can be reported in newspapers without fear of contempt.

He said: "Four rebel MPs asked questions giving the identity of 'Colonel B', granted anonymity by a judge on grounds of 'national security'. The DPP threatened the press might be prosecuted for contempt, but most published."

The right to report parliament was the subject of many struggles in the 18th century, with the MP and journalist John Wilkes fighting every authority – up to the king – over the right to keep the public informed. After Wilkes's battle, wrote the historian Robert Hargreaves, "it gradually became accepted that the public had a constitutional right to know what their elected representatives were up to".